1. Field of the Invention
Embodiments of the present invention relate to a sheet inverting device and an image forming apparatus incorporating the sheet inverting device, more particularly to a sheet inverting device that reverses or turns over sheet-like recording media to expose a front side and then an opposite side for image formation, and an image forming apparatus, such as a copier, printer, facsimile machine, plotter, inkjet printer, and a multifunctional machine including at least two of functions of the copier, printer, facsimile machine, plotter, and inkjet printer, which incorporates the sheet inverting device.
2. Description of the Related Art
A wide variety of image forming apparatuses incorporating an automatic duplex printing function that forms and prints images on front and opposite sides of a sheet also include a sheet inverting device that can switch the sheet back to turn over the front side and the opposite side of the sheet.
It is generally known that sheet inverting devices expose the leading edge of a sheet having a first image formed on a front side thereof to the outside to reverse the sheet for printing either a second image on an opposite side thereof, switch back the sheet with a pair of sheet discharging rollers that can rotate in forward and reverse directions to convey the sheet in a reversing pathway (or a duplex side feed pathway) for turning over the first side having the printed first image thereon, print the second image on the second side thereof in an image forming unit where the first image has been printed on the first side of the sheet, and discharge the sheet with the pair of sheet discharging rollers to a sheet discharging tray.
It is also known that sheet inverting devices convey a sheet into a sheet reversing pathway and then reverse a direction of rotation of a pair of sheet reversing rollers to convey the sheet from the sheet reversing pathway to another pathway for turning over the sheet.
For the purpose of forming the reversing pathway of a duplex conveyance unit that can process a long-length sheet without increasing a width or a height of the image forming apparatus, Japanese Patent Application Publication No. JP-11-092041-A discloses an image forming apparatus that includes a sheet refeed pathway and a sheet reversing pathway. The sheet refeed pathway extends vertically to convey the sheet with an image on the first side thereof in a duplex conveyance unit toward a refeed sheet entrance to an image forming unit. The sheet reversing pathway extends parallel to the sheet refeed pathway. The sheet refeed pathway and the sheet reversing pathway merge in a vicinity of the refeed sheet entrance.
By contrast, Japan Patent No. 3620993 is known to have a method for reversing a sheet without providing the sheet reversing pathway. The sheet is then exposed to the outside from the sheet discharging exit and then taken into the device again so as to turn the sheet over.
Further, for encouraging improvement of productivity of digital image forming apparatuses performing duplex printing of multiple sheets of paper, it is known to employ an interleaving method as a duplex printing method as disclosed in Japanese Patent No. JP 3780193, for example. In the interleaving method, after a front side of a first sheet is printed, the first sheet is inverted and conveyed to the image forming section again so as to print an image on an opposite side thereof. The interleaving method uses this period of time, that is, performs printing of a front side of a second sheet, in the period in which both faces of the first sheet are printed.